Immersion Foot

Immersion foot (trench foot, non-freezing cold injury) is a nerve and vascular injury from prolonged exposure of the feet, and sometimes the hands, to cold, wet conditions at temperatures between 0 and 15 degrees C, without tissue freezing. It affects soldiers, hikers, climbers, farm workers, homeless people, fishermen, and anyone in wet boots for more than 12 hours. In warm water, tropical immersion foot results from 48 hours or more in water at 20 to 30 degrees C.

Cold causes vasoconstriction with prolonged tissue ischaemia and endothelial injury, followed by rewarming vasodilatation, oedema and reperfusion injury, and damage to small nerve fibres (axonal and demyelinating), leading to chronic neuropathy and cold hypersensitivity. Unlike frostbite, the tissue remains unfrozen, but long term sequelae are common: in about 70 percent of severe cases symptoms persist beyond a year. Risk factors are tight, wet footwear, immobility, smoking, diabetes, peripheral vascular disease, alcohol, and previous cold injury.

• Phase 1 (during exposure): cold, numb, heavy, pale or mottled feet.
• Phase 2 (hyperaemic, hours to days after rewarming): swollen, red, hot, intensely painful (burning, shooting) feet; blisters, bullae, ulceration, lymphangitis, and in severe cases superficial gangrene.
• Phase 3 (post-hyperaemic, after 2 to 6 weeks): cold, blue, sweating feet with paraesthesia, hyperaesthesia, vasospasm on cold exposure.
• Chronic: neuropathic pain, cold hypersensitivity, hyperhidrosis, nail changes, weakness, impaired balance and joint stiffness, tissue loss in a minority.
• Red flags: gangrene, cellulitis, systemic sepsis, compartment syndrome, rhabdomyolysis, and tetanus.

• Clinical diagnosis from exposure history (duration, temperature, wet footwear) with typical features.
• Examination: capillary refill, pulses (Doppler ankle brachial index), sensation to monofilament and pinprick, temperature differences, signs of infection.
• Quantitative sensory testing and thermography for cold sensitivity; nerve conduction studies for small fibre neuropathy (often normal), skin biopsy for intra epidermal nerve fibre density when diagnosis is uncertain.
• Laboratory: full blood count, glucose and HbA1c, creatine kinase, urea and creatinine, C-reactive protein.
• Doppler or duplex imaging for arterial occlusion; angiography when ischaemia is suspected.
• Exclude frostbite, peripheral arterial disease, diabetic neuropathy, erythromelalgia, vasculitis, cellulitis, deep vein thrombosis, and gout.

• Remove wet footwear and socks; dry the feet gently and keep them at room temperature (20 to 25 degrees C), uncovered and elevated; do not rewarm quickly, do not apply direct heat, hot water or massage, and do not rub or soak, because rapid warming worsens pain and injury.
• Analgesia: paracetamol 1 g orally every 6 hours; for burning pain amitriptyline 10 mg orally at night, increased by 10 mg every week to 50 to 75 mg, or gabapentin 300 mg orally at night, increased to 300 mg three times daily then to 600 mg three times daily as tolerated; pregabalin 75 mg twice daily increased to 150 mg twice daily after 1 week is an alternative. Avoid non-steroidal drugs routinely in the hyperaemic phase unless pain control requires them (ibuprofen 400 mg three times daily with food for 7 days).
• Blisters: leave intact; if ruptured, clean with chlorhexidine 0.05 percent and apply non-adherent dressing; no weight bearing until healed.
• Infection: flucloxacillin 500 mg orally every 6 hours for 7 days (children 12.5 to 25 mg/kg every 6 hours); if penicillin allergic, clindamycin 450 mg every 8 hours for 7 days; tetanus toxoid 0.5 mL intramuscularly if not immunised in the last 5 years.
• Vasospasm: nifedipine modified release 20 mg orally twice daily for 3 months (stop if hypotension, headache, or ankle oedema), or amlodipine 5 to 10 mg once daily.
• Pentoxifylline 400 mg orally three times daily for 3 months may improve the microcirculation.
• Gangrene: allow auto demarcation for 4 to 12 weeks before amputation, unless wet gangrene or sepsis demands immediate surgery.
• Rehabilitation: bed rest for 3 to 5 days, graded return to weight bearing activity, physiotherapy, occupational therapy, and psychological support; modified footwear and insulated socks.
• Follow up: weekly during recovery, then at 3 months and 12 months for persistent cold sensitivity or neuropathic pain; refer for specialist assessment if symptoms exceed 3 months.
• Prevention: change socks at least twice daily, use waterproof boots with insulation, keep feet dry and mobile every 30 minutes, stop smoking, and adjust duty cycles in cold, wet work. Previously injured people are at higher risk and should be counselled to avoid cold work.